An efficient Ru^II-Rh^III-Ru^II polypyridyl photocatalyst for visible-light-driven hydrogen production in aqueous solution

The development of multicomponent molecular systems for the photocatalytic reduction of water to hydrogen has experienced considerable growth since the end of the 1970s. Recently, with the aim of improving the efficiency of the catalysis, single-component photocatalysts have been developed in which the photosensitizer is chemically coupled to the hydrogen-evolving catalyst in the same molecule through a bridging ligand. Until now, none of these photocatalysts has operated efficiently in pure aqueous solution: a highly desirable medium for energy-conversion applications. Herein, we introduce a new ruthenium-rhodium polypyridyl complex as the first efficient homogeneous photocatalyst for H ₂ production in water with turnover numbers of several hundred. This study also demonstrates unambiguously that the catalytic performance of such systems linked through a nonconjugated bridge is significantly improved as compared to that of a mixture of the separate components. Hydrogen evolution in water: An efficient homogeneous single-component Ru₂Rh photocatalyst promoted H₂ evolution in fully aqueous solution in the presence of ascorbate as a sacrificial electron donor with turnover numbers (TONs) up to 430 (see picture). The catalytic performance of the linked system with a nonconjugated bridge was significantly improved as compared to that of a mixture of the separate components.